21st Century Astronomy
6th Edition
ISBN: 9780393428063
Author: Kay
Publisher: NORTON
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Question
Chapter 22, Problem 38QP
To determine
The average density of the Milky Way and compare with it with the critical density.
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The density profile of a galaxy's extended dark matter halo is given in the provided image. r0 and ρ0 are both constant. r is the distance from the center of the halo. Find the mass of dark matter inside a sphere with radius R around the center.
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Chapter 22 Solutions
21st Century Astronomy
Ch. 22.1 - Prob. 22.1CYUCh. 22.2 - Prob. 22.2CYUCh. 22.3 - Prob. 22.3CYUCh. 22.4 - Prob. 22.4CYUCh. 22.5 - Prob. 22.5CYUCh. 22 - Prob. 1QPCh. 22 - Prob. 2QPCh. 22 - Prob. 3QPCh. 22 - Prob. 4QPCh. 22 - Prob. 5QP
Ch. 22 - Prob. 6QPCh. 22 - Prob. 7QPCh. 22 - Prob. 8QPCh. 22 - Prob. 9QPCh. 22 - Prob. 10QPCh. 22 - Prob. 11QPCh. 22 - Prob. 12QPCh. 22 - Prob. 13QPCh. 22 - Prob. 14QPCh. 22 - Prob. 15QPCh. 22 - Prob. 16QPCh. 22 - Prob. 17QPCh. 22 - Prob. 18QPCh. 22 - Prob. 19QPCh. 22 - Prob. 20QPCh. 22 - Prob. 21QPCh. 22 - Prob. 22QPCh. 22 - Prob. 24QPCh. 22 - Prob. 28QPCh. 22 - Prob. 29QPCh. 22 - Prob. 31QPCh. 22 - Prob. 32QPCh. 22 - Prob. 33QPCh. 22 - Prob. 34QPCh. 22 - Prob. 35QPCh. 22 - Prob. 36QPCh. 22 - Prob. 37QPCh. 22 - Prob. 38QPCh. 22 - Prob. 39QPCh. 22 - Prob. 40QPCh. 22 - Prob. 41QPCh. 22 - Prob. 42QPCh. 22 - Prob. 43QPCh. 22 - Prob. 44QPCh. 22 - Prob. 45QP
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- What are the two best ways to measure the distance to a distant, isolated spiral galaxy, and how would it be measured?arrow_forwardWhat does it mean if one elliptical galaxy has broader spectrum lines than another elliptical galaxy?arrow_forwardWhy could the concentration of matter at the center of an active galaxy like M87 not be made of stars?arrow_forward
- Why were quasars and active galaxies not initially recognized as being “special” in some way?arrow_forwardWhat are the two best ways to measure the distance to a nearby spiral galaxy, and how would it be measured?arrow_forwardIf we see a double image of a quasar produced by a gravitational lens and can obtain a spectrum of the galaxy that is acting as the gravitational lens, we can then put limits on the distance to the quasar. Explain how.arrow_forward
- Astronomers estimate the mass of the stars in a certain galaxy to be about 3.040 kg, and the total mass of this galaxy to be about 1.241 kg. The amount of the galaxy's mass is made up of dark matter is percentarrow_forwardhow long do long-exposure photos of two selected areas of the sky reveal that galaxies are very common?arrow_forwardObservations of quasars have shown us that many are extremely _________, emitting more energy than all the stars in a galaxy. The energy they give off comes from a very small volume, typically about the size of ___________. Some have long ______, shooting off in opposite directions. Today, astronomers understand that all the properties of quasars can be explained if they are __________ at the centers of galaxies. Astronomers can use _____________ to study images and spectra of the central regions of galaxies more clearly than earlier instruments.arrow_forward
- Assume that the average galaxy contains 1011MSunand that the average distance between galaxies is 10 million light-years. Calculate the average density of matter (mass per unit volume) in galaxies. What fraction is this of the critical density we calculated in the chapter?arrow_forwardAccording to Hubble’s law, what is the recessional velocity of a galaxy that is 108 light-years away from us? (Assume a Hubble constant of 22 km/s per million light-years.)arrow_forwardWhy are quasars generally so much more luminous (why do they put out so much more energy) than active galaxies?arrow_forward
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